1. Field of the Invention
The invention relates to an explosion-proof device with a pressure-proof capsule, an electronic means and a signal receiver, wherein the electronic means is designed to be intrinsically safe, the pressure-proof capsule has a radiolucent process window and the signal receiver is arranged inside of the pressure-proof capsule.
2. Description of Related Art
By an explosion-proof device, it is meant that a device is suitable for operation in areas with an explosive atmosphere. The radiolucent process window is permeable to at least a certain range of the electromagnetic spectrum, which the explosion-proof device can receive with the signal receiver. In particular, the radiolucent process window can be permeable to electromagnetic radiation, such as, e.g., visible light, infrared-, microwave-, radar-, X-ray, gamma- and ultraviolet radiation. It is also possible that the radiolucent process window is permeable to radiation that consists of particles, such as, e.g., alpha- and beta-radiation. This radiation can be then detected by the signal receiver. The explosion-proof device thus generally serves to detect radiation signals that are emitted by a process positioned on the side of the radiolucent process window not facing the electronic means. A radiation signal can merely consist of the radiation to be detected, being either present or not. A process can, for example, be a substance or mixture of substances in an aggregate state or multiple arbitrary aggregate states whose characteristics, presence or dynamics are to be monitored, determined or influenced.
Provisions for the construction and testing of intrinsically safe operating means that are determined for use in a field having gas explosion risks, as well as for corresponding operating means that are intended for connection to intrinsically safe electric circuits that are inserted into such areas are specified by the standard EN 60079-11 “explosive atmosphere—part 11: device protection by intrinsic safety ‘I’.” This standard also applies to electric operating means or parts of electric operating means that are located outside of the area at risk for gas explosion or are protected by another type of ignition protection in accordance with EN 60070-0, insofar as the intrinsic safety of the electric circuit in the area at risk for gas explosion is dependent on the design and construction of this electric operating means or of parts of this operating means.
The ignition protection intrinsic safety is based on the limitation of electric energy within operating means and connecting pipes that are subject to an explosive atmosphere at a level below that at which ignition can occur due either to spark formation or heating.
A further possible type of protection is the pressure-proof encapsulation. In this type of protection, also called “ex-d”, the explosion protection is ensured by explosions possibly occurring within the capsule being shielded by the pressure-proof capsule in such a manner that a prevailing explosive atmosphere outside of the pressure-proof capsule is not ignited. Accesses in the wall of the capsule, thus, have to have an ignition spark resistant gap. The surface temperature of the capsule should not reach the ignition temperature of the surrounding explosive atmosphere in the case of an expected error. The standard EN 60079-1 “explosive atmospheres—part 1: device protection by pressure-proof encapsulation ‘d’” specifies the requirements of operating means of this type of ignition protection.
A comparable principle of encapsulation similar to pressure-proof encapsulation ignition protection is molded encapsulation ignition protection, also called “ex-m.” In molded encapsulation, components that could represent a potential source of ignition are coated with a casting compound suitable for this application. Using these measures, it is ensured that the surrounding explosive atmosphere does not come into contact with these components. In molded encapsulation ignition protection, the surface temperature should also not reach the ignition temperature of the surrounding explosive atmosphere in the case of an expected error. The standard EN 60079-18 “explosive atmosphere—part 18: device protection by molded encapsulation ‘ex-m’” specifies the requirements for operating means of this type of ignition protection.
Devices known from the prior art are either designed in only one type of ignition protection, such as, e.g., pressure-proof encapsulation “ex-d” or intrinsically safe “ex-i” or are a mixture of forms in which the parts of the device are designed in a first type of ignition protection and other parts of the device are formed in another type of ignition protection.
An explosion-proof magnetic flowmeter is known from German Patent Application DE 37 11 754 A1 having a fittings pipe that can be installed in a pipeline with at least one measuring electrode on the inside of the pipe and at least one electromagnet assigned to the measuring electrode and constructed explosion-proof and joined to the fittings pipe, with an electric supply unit for supplying power to the magnetic coils and evaluation electronics, and a protective housing surrounding the supply unit. Here, the electric supply unit is separate from the intrinsically safe evaluation electronics within the protective housing in its own explosion-proof capsule, with cable entries for electric supply and cable exits for power supply to the magnetic coil and the evaluation electronics.
An essential disadvantage that results from the prior art is that connections from one part of a device, which is designed in a first type of ignition protection, to another part of a device, which is designed in another type of ignition protection, are often very complicated. For example, cable accesses through the wall of a pressure-proof capsule are particularly complicated, since the gaps occurring here have to be designed flashback resistant. Furthermore, safety barriers are required for connections between parts of a device designed with intrinsic safety and other parts of the device, which are designed in another type of ignition protection so that the intrinsic safety of the part of the device designed with intrinsic safety can be further guaranteed.